1. Field of the Invention
This invention relates to polyorganosiloxane sealant and adhesive compositions which cure in the absence of oxygen. More specifically, the invention relates to polyorganosiloxane sealants which cure in the absence of oxygen and which have improved fixation and curing times, strength and thermal stability.
2. Description of Related Art
Anaerobically curing sealant compositions have been known for a long time. These compositions were however, limited to those based on polyalkylene ether polymerizable monomers and organic (meth)acrylate polymerizable monomers. Such compositions typically show poor thermal stability properties.
Because of their excellent thermal stability, silicones (polyorganosiloxanes) have been used for many sealant, adhesive and coating applications. However, because of large amounts of dissolved oxygen and high permeability to oxygen it was generally believed that silicones would not be anaerobically curable. U.S. Pat. No. 4,035,355 to Baney et al. teaches anaerobically curing sealant compositions of acrylate-containing polyorganosiloxanes and a hydroperoxy polymerization initiator. The Baney compositions are however, disadvantageous due to their relatively long cure time of approximately 24 hours.
U.S. Pat. No. 5,391,593 to Inoue et al. is directed to a silicone rubber sealant composition comprising an organopolysiloxane, an organic peroxide and carbon black which is said to cure under anaerobic conditions into silicone rubber having improved physical properties. These silicones do not however, fully cure until about 2 to 3 days after removal of oxygen. Japanese Kokai JP 04268315 to Toshiba Silicone Co, Ltd. is directed to an anaerobically and ultraviolet curable polyorganosiloxane composition for adhesive purposes that is reported as having good heat resistance. This composition is said to show adhesion after 2 hours.
Thus it would be a significant advance in the art to provide an anaerobically curing silicone composition that cures in a short period of time without sacrificing heat stability and strength properties of the cured resin.